Nofima

Analysing war and peace among bacteria

Pål Trosvik has developed new methods of understanding how microbial communities work. "Only when we understand this will we be able to control and manipulate them," he says. Trosvik has his doctoral disputation on Monday.

Through a unique inter-disciplinary collaboration between Nofima Mat (formerly Matforsk) and the Centre for Ecological and Evolutionary Synthesis (a designated Centre of Excellence at the Department of Biology at the University of Oslo) Pål Trosvik has developed new methods for measuring the incidence of various microbes in complex communities. This provides entirely new opportunities for understanding how microbial communities work, something of potentially great value in preventing and treating infections, for example.

Many bacteria – little knowledge

The bacteria live in complex communities, whether in earth, water or the human body. For example, the normal human bacterial flora consists of as many as 1014 bacteria cells, or about 100 times as many as there are human cells in the body. There is a growing body of literature documenting the significance these microbes have for health and disease. But our knowledge of their ecology is still very limited.

New applications

In ecological studies of plants and animals, much use is made of time series data. Time series analyses can provide information about the conditions that control the development of ecosystems, for example why lemming years occur at regular intervals or the mechanism behind the collapse of a fish stock.
Using this type of analysis to study the world of microbes is completely new. "One of the most important things I have achieved is to join together the disciplines of ecology and microbiology. I believe we have much to gain from working together," says Pål Trosvik.

Counting the invisible

Population data on microbes is difficult to obtain. While the ecologists can physically count deer or cod, bacteria are for practical purposes invisible (except in a microscope), difficult to tell apart and have extremely short generation times (as little as 10 minutes in favourable circumstances).
"The methods we have developed make it possible to follow microbial communities over time in a relatively rapid, cheap and simple way. They are based on the simultaneous registration of DNA molecules that can distinguish between the different members of a community. The DNA signals are then analysed using calculation methods that are normally used in chemistry," explains Trosvik.

The good defeat the bad

The methods have been tested both in infection situations in chickens and in laboratory cultures of intestinal bacteria. Analysis of the resulting time series has made it possible to create hypotheses about how microbial communities work. "This is important in order to be able to prevent diseases that arise following changes in the body’s natural bacterial flora in the intestine," says Trosvik. An example: In one study he looked at the interplay between representatives of four of the most important divisions of intestinal bacteria in humans, including Clostridium Perferingens (common cause of diseases carried in food products) and Bacteroides thetaiotaomicron (involved in a number of physiological functions in humans). It was shown that the internal competition between bacteria led to the "bad" clostridium bacterium being limited, while B.thetaiotaomicron favoured the growth of the "health" bacteria Bifidobacterium longum (which can be found in yoghurt products and similar).

Already in use

"What can this method be used for?"
"Basically it can be used on anything that has DNA, that you want to count and that occurs in mixtures. I count the relative quantities and it is the change over time that is important in these time series analyses," says the doctoral candidate.
The analysis method Trosvik has developed has already been well implemented at Nofima Mat and is now used in several research projects involving microbial communities. The scientific articles that have been written on this topic have received a great deal of attention in professional circles involved in human health and environment. Many are interested in collaboration. But what this will be about is something Pål Trosvik cannot disclose yet. He continues as a researcher with Nofima Mat and CEES after the disputation.

Pictures: Pål Trosvik
What happens to the bacteria in the intestine over time? If we understand this, we can prevent many diseases.